The CNRS Research Program on the Thorium cycle ... - Pacen - IN2P3

Thorium Cycle – Molten Salt Reactors June 2008
accumulated over two hundred years it will dominate the final waste. With the log scale used in Fig.17,
an operation of the fast TMSR-NM over 400 years instead of 200 which would induce an upward shift
of the three purple curves by less than a third of a division (factor 2), does not change this conclusion.
Thus, for societies which consider that the choice of a technology covering their present
energy needs must take into account their legacy to future generations, there is a definite incentive to
optimize global radiotoxicity including both the waste stream and the inventory. In that respect, finding
ways to reduce the radiotoxicity of the TMSR-NM inventory as one enters the End-of-Game phase to
the level of that of the accumulated waste stream is of major interest. For the TMSR-NM, this requires
a destruction of 233 U whose decay dominates the radiotoxicity of the inventory between 10 4 and 10 5
years.
Fig.17 Time evolution of several waste radio-toxicities. <strong>The</strong> purple dash curve at the top is the actinide
waste radiotoxicity resulting from 200 years of operation of a GEN-III reactor; i.e. a two century open
cycle. <strong>The</strong> green dash curve corresponds to the matters extracted from the spent fuel of a GEN-III
reactor which are used as the initial inventory of the TMSR-NM. <strong>The</strong> green dash-dot curve
corresponds to the contribution of the radioactive inventory of the fuel in a TMSR-NM core and its
recycling facility when the steady state has been reached. <strong>The</strong> green solid curve corresponds to the
transformed inventory after sixty additional years of incineration in a dedicated TMSR. <strong>The</strong> purple
dash-dot curve gives the accumulated actinide waste stream produced over 200 years of TMSR-NM
operation while the purple solid curve shows how this waste stream radiotoxicity is modified by the
contribution of the additional actinide waste stream during the 60 years devoted to reduction of the
inventory.
If a decision to abandon fission and to move over to a new technology is taken at some date in
the future 19 , apart from the decision to immediately consider the inventory as an ultimate waste to be
disposed of in a geological storage, it seems that the only acceptable alternative will be to work on the
destruction of this inventory. Should this choice be made, it is unlikely that it will be decided to design
and built an entirely novel system relying on fission for that sole purpose. On the other hand, as
Physics tells that low energy neutrons are by far the cheapest way to achieve the fission of actinides, it
seems reasonable to assume that one will try to hand this task over to an already available and welltested
fission-based technology albeit with a changed mission. Now, instead of the generation of
energy and brreding, the priority will be given to the incineration of as much as possible of the
inventory in order to reduce the burden on the storage 20 . This is a scenario that we have started to
investigate as another illustration of the versatility of the TMSR-NM concept.
To that aim, we consider a situation where, in fleet of TMSR-NMs which it has been decided to
stop, for every seven reactors 21 an incinerator TMSR is started which, over a sixty year period, will
burn the inventory of the 7 reactors. Keeping in mind that one of the criterions is the minimization of
technological untested innovations as one enters the End-of-Game phase, we choose a TMSR with
19
We assume that this novel technology does not rely on nuclear fission and has no use for the energy content of
actinides.
20
Of course, this incineration will also contribute to an additional production of energy
21
As a matter of fact the exact value of the ratio is 6.9 to 1 which for this preliminary study, we approximate as 7
to 1 for the sake of redaction simplicity.
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